There are many applications for which physical properties of a certain substance mixed with or included in another substance need to be determined to high accuracy. For example, in medical treatment, the density of particles in aqueous solutions has to be known in order to assure proper treatment or proper diagnosis. Also, it is needed to adjust the composition of a dialysate when a patient's renal deficiencies have to be compensated. Moreover, the volume percentage of water in a patient's blood has to be measured and monitored.
From the state of the art, methods and devices are known that are based on the principle of driven oscillations, i.e. they need an external transmitter and receiver. Such systems and devices, however, are disadvantageous.
Thus, the problem underlying the present invention was to provide a means of determining properties of a known particle kind within a composition of different kind of particles by using a more precise method that can be performed in a non-invasive manner.